1. Field of the Invention
The present invention relates to an improvement in a metal spraying method, i.e., spraying a desired metal on the surface of aluminum or aluminum alloy (both of which will be hereinafter referred to as an "aluminum material").
2. Description of the Prior Art
A variety of metal sprayings onto the surface of an aluminum material have been widely put into practice for various purposes. Since, however, aluminum is subject to the formation of an oxide layer on its surface, a sufficient adhesion between the metal-sprayed layer and the aluminum substrate cannot be obtained due to the existence of this oxide layer. As a result, the metal-sprayed layer will be susceptible to being peeled off, and as such little can be expected from the spraying of a layer onto the aluminum material.
In the current metal spraying method, which is widely employed in the art in order to improve the particular adhesive, effects a thin foundation coat is first created by spraying onto the aluminum material a highly adhesive metal such as nickel aluminide or molybdenum. Then, desired metal is sprayed onto the thin foundation coat, thus ensuring a considerably secure adhesion inbetween. In this conventional method, however, the metal spraying is performed on the aluminum material through its oxide layer, and the aforementioned difficulty due to the existence of the oxide layer is not solved. This is especially so when the metal-sprayed aluminum material is to be used in such sealing elements of an internal combustion engine as are exposed to severe working conditions under the circumstance the peeling-off of the sprayed metal layer from the substrate cannot be prevented in the least. Thus, the current metal spraying method can afford a satisfactory answer.